Because of superior processability, coloring ability and luster as well as superior impact resistance and strength, ABS resin is widely used for electric/electronic housings and automobile interior/exterior materials. When used for internal parts of a refrigerator, the ABS resin requires resistance against foaming agent in addition to the afore-mentioned properties.
It is because foaming agents, such as freon (CFC-11, HCFC-141b, HFC-245fa, HFC-245eb, HFC-245ca, HFC-356mffm) or cyclopentane, used to form urethane foams in making the insulation layer of a refrigerator may contact the resin during or after the manufacturing process, thereby causing chemical crack and cracking of the resin at the site where internal stress is concentrated.
As conventional methods of improving chemical resistance, increasing content of vinyl cyanide compound in ABS resin, increasing rubber content, increasing molecular weight of acrylonitrile-styrene copolymer resin (hereunder referred to as “SAN resin”), etc. are known. However, increasing content of vinyl cyanide compound may cause yellowing and reduced fluidity during processing of the resin. Increasing rubber content or increasing molecular weight of SAN resin may also cause worse resin processability.
Japanese Patent Laid-Open No. Hei 10-338794 introduces an ethylene-containing terpolymer in order to improve chemical resistance. But, thermal stability of the resin is lowered because the compound is decomposed at high temperature during compounding.
In order to solve the problem of the ABS resin composition, the present inventors developed a thermoplastic styrenic resin having superior chemical resistance by introducing a rubber graft copolymer.